The present invention generally relates to systems and methods for regulating voltage and, more particularly, to adaptive field control systems and methods for regulating the point-of-regulation voltage that controls power generation.
Electrical power for commercial and military application is typically generated by either an alternating current (AC) or a direct current (DC) generator that is controlled by regulating the voltage at a point-of-regulation (POR). A generator control unit (GCU) modulates the generator excitation current according to load and speed conditions to maintain a constant output voltage at the POR. The GCU must compensate for load transitions by increasing or decreasing the field current. If the load transition compensation is not achieved within a recovery time limit, the POR voltage could fall outside the customer power quality limits, thereby causing the utilization equipment malfunction and/or damage.
For aircraft with a traditional fixed frequency system that normally operates at 400 Hz, lack of adequate load transition compensation does pose a minor performance issue. However, this problem may pose a severe performance issue in the case of variable frequency systems, since the operating speed is wide ranging and varies, for example, from 10,000 rpm to 24,000 rpm.
Field discharge may be used to compensate the load transition conditions. A field discharge circuit may include a field switch and discharge resistance through which the energy is dissipated in short duration during load transitions. In conventional systems, the field discharge circuit is trigged based on the POR voltage, output current, or field current.
For example, when the POR voltage is greater than a certain limit, the field discharge circuit is engaged to dissipate the energy. Once the POR voltage drops to normal operating voltage, the field discharge circuit is disengaged.
There are disadvantages with conventional field discharge systems. The following are some of the problems and shortcomings of the presently known field discharge systems: a) the field discharge circuit is trigged based on a fixed POR voltage set point for all operating conditions; b) selecting a set point close to operating voltage condition will result in system oscillations during large motor load, non-motor load and unbalanced conditions; c) system oscillations can happen when the POR voltage varies outside of power quality specifications (less than the over voltage (OV) limit and greater than the under voltage (UV) limit), causing the field discharge to turn on and turn off continuously, which may result in overheating and damage of the field discharge resistance and other components in the voltage regulator; d) loss of field discharge function will result in system trip and controller damage under large load removal conditions; e) selecting the set point limit higher than or near to over voltage limit will not protect the system against the load transients; and f) damage in the voltage regulator will result in loss of electric power and impact the generator control unit reliability.
As can be seen, there is a need for reliable field discharge systems and methods that results in better field control throughout the entire speed and various operating conditions of variable frequency generator applications as compared to conventional systems and methods.